I understand, I have also done a whole lot of research and spent a lot of time talking to professionals who in the end weren't able to assure me of anything.Unfortunately i lost the account in the second stage after the Gauntlet, however i spent a crazy amount of time to figure things out about the ITIN and other related documents.
I live in Belgium and we also have a tax treaty with the USA, however this tax treaty only applies if you have an ITIN and report taxes to the US government and your own government.
Also make sure that the tax treaty Sweden has with the USA does cover this kind of income. Most likely it will cover it but better be safe than sorry.
I still think E2T and Helios are one of the best funding companies out there, the only reason i didn't went back is because of the complicated situation regarding the ITIN.
You are in good hands at E2T/Helios, just make sure to get a good accountant who has experience in doing business with the USA, you don't wont to get in trouble with IRS.
My biggest issue with the ITIN is sending my passport to the US. I live on the road with my girlfriend and sending it away would be crippling. Unfortunately the IRS states that a certified copy of the passport has to be granted by the issuing agency, which here in Sweden would be the police, yeah good luck with that.
I have also emailed a few people certified as publicus notarius which also weren't able to assure me if they certification would be accepted by the IRS and adviced me to ask the IRS. The problem there is that it is very hard to find a way to get in touch with the IRS since I do not yet even have a tax return to file and I am a foreign citizen.
Just typing this out gave me a headache. I am going to stick with my new plan which I outlined above.